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• • READ THIS FIRST IMPORTANT ♦ READ THIS FIRST A - Before beginning the actual assembly procedures, read and make sure you and all individuals involved in the in- stallation thoroughly understand the following sugges- tions and precautions: Matching taper angles for the spigot and the bell make it Matching taper angles allow the joint to mechanically lock possible to mechanically "lock up" a joint by wedging the up, producing a thin line of adhesive called a glue line. spigot into the bell. This produces a very thin line of ad- hesive called the bond line, or glue line, which is only a few thousandths of an inch thick. In all cases, the bonding surfaces must be clean and dry before applying adhesive. joint strength of the bell and spigot joint is essentially controlled by the adhesive thickness between the two matching tapered surfaces. The adhesive is relatively brit- tle in thick sections and fails easily if the bond line is too thick. The mechanical lock determines adhesive thick- ness. Joints that are not "locked up" during installation may pass an initial steady pressure test, but can fail premature- ly at a later date due to reduced bond strength caused by the thick adhesive. Therefore, it is essential that the in- stallation crew be familiar with the joint concept and un- derstand the importance of completely inserting and lock- ing the spigot into the bell. The mechanical locking of the joint is absolutely essential to develop the full strength of the joint. Using mechanical force (such as hammering against a wooden block placed against a fitting or bell end of pipe) helps achieve "lock up." Note: This is the same mechani- cal lock of matching tapers that is commonly used on ma- chine tools. For T.A.B.rm (threaded and bonded) joints, special T.A.B. wrenches are recommended to achieve the mechanical lock-up in the joint. Cool weather conditions require special precautions when bonding pipe and fittings. The adhesive is very viscous (thick) when it is cool or when it is applied to cool pipe. This thick adhesive can actually be stiff enough to prevent complete joint "lock up." There are different installation procedures for both warm and cool weather installations. This concept is often overlooked when a crew installs pip- ing when there are significant temperature variations throughout the day or week. All bonding surfaces must be factory fresh in appearance. When end caps have been lost, surfaces will weather and result in loss of bond strength. When surfaces are weath- ered, retaper spigots and sand bells to achieve a factory fresh appearance (see Part One, Section 8). NOTE: T.A.B. COUPLINGS THAT HAVE BEEN WEATHERED MUST BE REPLACED. RED THREAD IIA Pipe br Fittings Bonding surfaces must be clean and dry. Joint strength is controlled by the adhesive thickness -thick is bad, thin is better. Mechanical locking of the joint is absolutely essential to develop full strength of the joint. Using mechanical force helps achieve joint lock up. Follow the appropriate installation procedures for warm or cool weather. All bonding surfaces must be factory fresh in appearance.